Northern Rockies Fisher

Northern Rockies Fisher, USFWS Photo

(Pekania pennanti)

Physical Characteristics: 31-40 inches long, 3-13 pounds. The Fisher, a member of the weasel family, has a face that is fox-like, with rounded ears and a pointed snout. It is a slim, bushy-tailed predator, blackish or dark brown and grizzled with white on the head. Overall, it somewhat resembles a dark, overgrown squirrel. Males are about 20 percent larger than females.

Diet: A solitary, opportunistic hunter, the Fisher preys on squirrels, hares, mice, muskrats, grouse, and other birds. It is notable in its ability to hunt the Common Porcupine, which it kills by repeatedly attacking the head or deftly rolling the animal over and attacking the unarmed underside. Though the Fisher is a good swimmer, contrary to its name it rarely eats fish. It will supplement its diet with insects, nuts, berries, and mushrooms, and is not averse to eating carrion.

Habitat: Fishers prefer old-growth, dense, coniferous forest. It is usually not found in young forests or where logging or fire has thinned the trees. Hollow trees and logs, brush piles, rock crevices, and cavities beneath boulders all serve as den sites, most of which are temporary as the Fisher is always on the move throughout its extensive home territory. The natal den is more permanent and usually located in a safe place like a hollow tree. In the winter, a den may be excavated in the snow.

Range: The Fisher is only found in North America. It is common in the Northeast and Midwest, but is one of the rarest carnivores in the Northern Rockies and Northwest. The populations in the Clearwater are genetically unique, as they descended from Fishers that have been in the area for generations, rather than, as previously believed, from Fishers reintroduced to north-central Idaho in the 1960s. The Clearwater fishers are thought to be the healthiest population in the West.

Reproduction: The reproductive cycle of the fisher lasts almost the entire year. Female fishers give birth to a litter of three or four kits in the spring. They nurse and care for their kits in the den for at least seven weeks. When they are three months old they begin to hunt with their mother, and by fall are independent. Females enter estrus shortly after giving birth and leave the den to find a mate. Implantation is delayed until the following spring when they give birth and the cycle is renewed.

Threats: Fishers are creatures of deep, untouched wilderness, and often disappear shortly after development begins in their range. Clearing of forests, habitat destruction, fires, and over-trapping resulted in its decline or extirpation. Climate change could increase the frequency of forest fires in its range, removing the older, cavity-bearing trees it needs for denning. Currently, the Fisher is not protected as an endangered or threatened species, despite its population dipping to a staggeringly low 500 individuals in Idaho and Montana.

Miscellaneous: The Fisher is one of the most formidable predators in the Rocky Mountains, and it could be considered the most athletic of this region’s carnivores. Fishers are particularly nimble in trees, and the anatomy of their ankles allows the feet to rotate sufficiently that a fisher can descend trees headfirst. Interestingly, their noted ability to hunt porcupine makes them of value to timber companies, as Fishers can reduce tree damage caused by porcupines.